1. Technical Field
The present invention relates to a secondary battery unit, and more particularly, to a secondary battery unit having two or more interconnected individual pouch type secondary battery cells, the battery unit having a single safety circuit board for all of the individual battery cells in the battery unit, the single safety circuit board not adding size, volume or bulk of the battery unit.
2. Related Art
Conventionally, secondary batteries have a small size and a high storage capacity, in addition to being rechargeable. Representative examples of such secondary batteries include nickel-hydrogen (Ni-MH) batteries and lithium (Li) secondary batteries.
According to the shapes of a case for accommodating a battery body, secondary batteries are classified as cylindrical batteries using cylindrical aluminum cans, prismatic batteries using prismatic aluminum cans, and pouch-type batteries using thin pouch-type cases.
Among them, the pouch-type secondary batteries has a battery body for generating a predetermined electric current and a pouch-type case for enclosing the battery body. The battery body further has a lead, which is connected to an electrode tab extended from a side of the battery body, to provide an electrical passage to the outside. Some parts of the lead are installed to be exposed from the pouch-type case.
The pouch-type case has a case body having a space for accommodating the battery body, and a case cover extending from an end of the case body and forming an integral structure with the case body. The edges of the case body are formed with flanges to seal the case body by coupling the case body with the case cover.
The pouch-type case of a pouch-type secondary battery with the above-described structure is made up of a mixed sheet of a metal foil and resin layers. By way of example, a pouch-type case is with aluminum foil may be formed by pressing together aluminum foil, a thermal adhesive layer and a resin layer. The thermal adhesive layer is formed at an inner surface of the aluminum foil. The thermal adhesive layer and the resin layer are sequentially formed at an outer surface of the aluminum foil. The thermal adhesive layer is made up of a polymer resin including modified polypropylene such as casted polypropylene (CPP). The resin layer is made up of nylon and polyethylene terephthalate. There exist pouch-type cases with various shapes including those as disclosed in U.S. Pat. Nos. 6,042,966 and 6,106,973.
Generally, the pouch-type secondary batteries with the above-described structure have a small storage capacity, and thus, are interconnected in parallel or series when used in electronic devices with a relatively high consumption of electric power such as notebook computers.
Meanwhile, the pouch-type secondary batteries further have a safety device for preventing explosion of the batteries due to a gas generated by an overcharge or an interelectrode short when charged or discharged. The safety device may be a safety circuit board with a positive temperature coefficient (PTC) device, and a safety vent, which is installed at a side of the case to change its structure according to the internal pressure of the case. The safety circuit board may be installed in each battery. Alternatively, in a case where multiple battery cells are interconnected in parallel or series, a single safety circuit board may be employed, the single circuit board being electrically connected to the terminals of each individual battery cell in a battery unit, which connects with electrode terminals of individual battery cells.
In this case, however, lead wires are required for connecting the safety circuit board with the electrode terminals of individual battery cells, and the installation of the safety circuit board produces many limitations. In particular, in the case where secondary battery cells are used in portable electric devices, the volume of the battery unit increases as a result of the area occupied by the safety circuit board. Therefore, it is difficult to limit the size of a secondary battery unit having multiple secondary battery cells interconnected in series or parallel via the safety circuit board.
One example of a battery unit comprising multiple secondary battery cells interconnected in parallel or series is disclosed in Korean Patent Laid-Open Publication No. 1999-54989. The battery unit comprises multiple individual battery cells are interconnected in parallel or series, each individual battery cell having alternately laminated multiple positive electrodes and multiple negative electrodes, which are separated by separators. The battery unit has a positive electrode connecting means for connecting the multiple positive electrodes to each other and negative electrode connecting means for connecting the multiple negative electrodes to each other.
Korean Patent Laid-Open Publication No. 1999-5862 discloses a secondary battery with an improved energy density by interconnecting in parallel electrodes with an integral structure of a current collector and an electrode terminal.
In the above-described secondary battery units, a separate safety circuit board must be installed at the side or front part of each battery cell, and thus, it is difficult to decrease the size of the battery unit.